The present invention relates to enhancing the quality of speech in a telephone call and, more particularly, to a method and apparatus that provides a flash-cut of speech processing features in a telephone call.
It is well-known in the telecommunication art to apply speech processing features in a telephone network in order to enhance the quality of the speech signals. Some features provide virtually their full intended effect immediately upon activation. These features are referred to as xe2x80x9cnon-adaptivexe2x80x9d and include, for example, pre-emphasis filters and equalizers. Other features, however, gradually and smoothly apply their effect, i.e., xe2x80x9cramp-up,xe2x80x9d following activation. These features are referred to as xe2x80x9cadaptivexe2x80x9d and include, for example, automatic gain control, background noise compensation, noise reduction and echo cancellation.
It is known that more than one speech processing feature can be applied in a telephone network. For example, U.S. Pat. No. 5,195,132 issued to Bowker et al. on Mar. 16, 1993 discloses utilizing both echo cancellation and digital filtering to enhance speech signal quality. However, a problem which heretofore has not been recognized in the telecommunication art arises when more than one speech processing feature is applied to a telephone network, especially with telephone networks using echo cancelers. This problem can be seen in FIG. 1 which shows a graph of a particular telephone call beginning at time t0. Curve 8 represents echo cancellation on the network. As is known in the art, echo cancellation requires time following the start of a call to fully xe2x80x9cramp-upxe2x80x9d or converge, and in FIG. 1 convergence of curve 8 occurs at time t1. Curve 9 represents another adaptive process such as background noise compensation which takes a duration of time t2 to ramp-up. A problem ensues throughout the duration of time t1-t0 when the ramp-up of both processes overlap. During this period the processes interfere with each other and the call quality is severely degraded. Therefore, there is a need for a technique for providing multiple speech processing features to a telephone network without having the call quality initially degraded.
Another problem with the techniques disclosed in the prior art for applying speech processing features to a telephone network involves the user""s perception of the effect of these features. In the telecommunication industry, speech processing features have always been provided at the start of the call and the motivation of telecommunication system designers has always been to reduce the ramp-up time of the features so that the transition to full effectiveness of the features is least noticeable by the customer. For example, U.S. Pat. No. 5,001,701 issued to Gay on Mar. 19, 1991 discloses using real-time allocation among subbands to achieve faster overall convergence of echo cancellation. However, we have found that if the speech processing features are provided right from the start of the call, with quick ramp-up time, users may not attribute the higher quality call to the presence of the speech processing features. Therefore, there is a need to alert the user that speech processing features that enhance the speech signal quality are being applied to a particular call.
In accordance with one embodiment of the present invention, two speech processing features are applied to the speech signals of a telephone call. However, the user only hears speech signals affected by one speech processing feature until both features have fully converged or ramped-up, and the two features are no longer interfering with each other. At that point, a xe2x80x9cflash-cutxe2x80x9d of the second speech processing feature is activated. The flash-cut instantaneously switches to speech signals affected by both features. This quick transition makes the speech processing features more noticeable to the user, and the user is not subjected to the period where the features interfere.
In another embodiment of the present invention, two speech processing features are applied to the speech signals of a telephone call. However, the user hears speech signals not affected by either speech processing feature until both features have fully converged or ramped-up, and the two features are no longer interfering with each other. At that point, a xe2x80x9cflash-cutxe2x80x9dof both speech processing features is activated.
In another embodiment of the present invention, an audio indicator is generated before implementing the flash-cut, so the user is alerted to the flash-cut, and the speech processing features are even more noticeable.
The above-described features of the present invention are not found in the prior art because the conventional wisdom in the telecommunication art is to minimize as much as possible the intrusiveness and noticeability to the user of the speech processing features. In contrast, in the present invention the flash cut and audio indicator increases the intrusiveness and noticeability of the speech processing features.